Search

A polymer electrolyte membrane is a core component of proton exchange membrane fuel cell. Since the ionic conductivity of polymer electrolyte membrane depends on water content, it is necessary to understand the water transport mechanism in the polymer electrolyte membrane. When the electric current demand is varied rapidly, the transient water transport results in the shortage or flooding in the polymer electrolyte membrane. The transient behavior of water transport in the polymer electrolyte membrane is nonlinear due to the water sorption/desorption mechanism. In this study, the nonlinear water transport mechanism of polymer electrolyte membrane is established to understand the transient behavior of water transport over the rapid change of electric current. Since the nonlinear dynamics delay the response of water transport under rapid change of electric current, system-level simulation is conducted to evaluate the system response by delayed water transport. Results show that the rapid change of electric current dramatically affects the water transport dynamics. As a result, this study confirms that water transport in the electrode is delayed depending on the polymer electrolyte membrane (PEM) thickness and that flooding occurs in the cathode depending on the relative humidity at the anode inlet. [ABSTRACT FROM AUTHOR]

With the development of autonomous driving and vehicular network,more and more vehicles will have powerful computing capabilities and connection with each other via wireless network.These computing resources can not only be applied to automatic driving,but also provide a wide range of edge computing services.Aiming at the task offloading among vehicles,a distributed task offloading algorithm based on online learning was proposed to minimize the average offloading delay.Furthermore,a system-level simulation platform was built to evaluate the impact of vehicle density and number of tasks on the average offloading delay in both highway and urban scenarios.The results provide a reference for the resource allocation and deployment of task offloading in different traffic situations.

The fifth-generation (5G) radio networks will support ultra-reliable low-latency communications (URLLC). In the uplink, the latency can be reduced by removing the time-consuming and error-prone scheduling procedure and, instead, using the grant-free (GF) transmissions. Reaching the strict URLLC reliability requirements with GF transmissions is, however, particularly challenging due to the wireless channel uncertainties and interference from other URLLC devices. As a consequence, the supported URLLC capacity and, hence, the spectral efficiency are typically low. Multi-cell reception, i.e., joint reception and combining by multiple base-stations (BS), is a technique known from long-term evolution (LTE), with the potential to greatly enhance the reliability. This paper proposes the use of multi-cell reception to increase the URLLC spectral efficiency while satisfying the strict requirements using GF transmissions in a 5G new radio (NR) scenario. We evaluate the achievable URLLC capacity for an elaborate multi-cell reception parameter space and multi-cell combining techniques. In addition, we demonstrate that rethinking of the radio resource management (RRM) in the presence of multi-cell reception is needed to unleash the full potential of multi-cell reception in the context of UL GF URLLC. It is observed that multi-cell reception, compared to a single-cell reception, can provide URLLC capacity gains from 205% to 440% when the BSs are equipped with two receive antennas and 53% to 22% when BSs are equipped with four receive antennas, depending on whether the retransmissions are enabled.

To generate training data for fault detection and diagnosis based on machine learning, a System-Level Simulation (SLS) is developed to model the global behavior of a reusable liquid rocket engine employing the expander-bleed cycle. Model parameters are estimated automatically by an Ensemble Kalman Filter. Parameters are estimated starting from the turbopump component model, followed by the whole rocket engine model, to increase accuracy. Sufficient convergence is obtained within one day by parallelizing the SLS computation for the ensemble members by two. Compared to the static-firing test results, reasonable agreement is obtained within error of 2.3% in the steady-state engine condition. Even for the startup and shutdown sequences, the present SLS reasonably agrees with the test results except for the temperature. Comparing the model parameters obtained for different static-firing test results, the effect of the overhaul inspection on the turbopump is captured as a difference in the model parameters. • A system-level simulation is developed to model a reusable liquid rocket engine. • Model parameters are automatically estimated by an Ensemble Kalman Filter. • Simulation results are agreed with static-firing test results within error of 2.3%. • The state change of the engine is captured as a difference in the model parameters. [ABSTRACT FROM AUTHOR]

3GPP is now carrying forward the development of the point to multipoint transmission mode of 5G on the basis of the cellular infrastructure and standard. Since the dedicated proposal for multimedia broadcast multicast system (MBMS) was approved, the MBMS technologies are evolving with the update of the requirements from 3G to 5G. This paper reviews the latest progress during the evolved MBMS standardization, which focuses on the LTE-based 5G terrestrial broadcast mode. Some agreements in terms of two widely discussed topics during 3GPP meetings, cell acquisition subframe (CAS) enhancement and numerology refinement, are presented. The enhancement of CAS and the update of numerology aim to deal with the service outage issue in the case of covering large area and serving high-mobility users. To verify the improvement brought by the CAS enhancement and the new numerology, simulations from system level and link level are carried out by several organizations and the representative results are presented and analyzed in this paper. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the performance of Heterogeneous Networks (HetNets) that are operating under Almost Blank Subframes (ABS) and Cell Range Expansion (CRE) by taking into consideration the effect of geographical information. In order to achieve such analyses, we develope a simulator that incorporates data from a Geographic Information System (GIS); specifically, a set of parameters that define the morphology of buildings and streets in urban areas. We describe the implemented methods to estimate the received power, as well as the average throughput, over an area of interest. Our numerical results clearly demonstrate that the overall network performance significantly depends on geographical information; hence our main contribution consists in developing a simulator that incorporates such information in the analysis and evaluation of ABS-CRE HetNets, which allows proposing design guidelines to improve the performance of these networks in realistic scenarios. To the best of our knowledge, this kind of proposal has not been reported in previous works. [ABSTRACT FROM AUTHOR]

System level simulations, which are gaining on importance in the product concept design process and in the "Hardware‐in‐the‐Loop" (HiL) applications, require models that feature high level of accuracy, high level of prediction capability and short computational times. This paper presents an innovative mechanistic quasi 3D model capable of real time computation of steady state and transient fuel cell operation. This model relies on a hybrid 3D analytic‐numerical model (HAN) approach, which models species transport by taking 1D numerical model for pipe gas‐flow and superimposing onto it a 2D analytic solution for concentration and velocity distribution in the plane perpendicular to the gas‐flow. The main innovative contribution of this paper comprises a significant mathematical reduction of the previously published HAN approach to a computationally optimized approach featuring a minimal amount of computational points yielding a real‐time capable model (denoted HAN‐RT), which complies with 1kHz HiL constraints while retaining HAN's quasi 3D nature. Presented results confirm that the computationally optimized HAN‐RT model displays real‐time capabilities at sampling rates above 1 kHz while producing results that agree very well with spatially resolved results generated by the 3D multiphase CFD tool and with the experimental results of steady state and transient fuel cell operation. [ABSTRACT FROM AUTHOR]

The use of dynamic TDD technology in heterogeneous network can effectively increase the system throughput and improve the performance of the system.Due to the limitation of signaling control and other issues,there is usually a dynamic switching between the traditional seven fixed sub-frame ratios in the licensed bands.But as a complement to the LTE system worked in the licensed bands,the unlicensed bands can achieve a more flexible and complete dynamic sub-frame configuration without considering signaling control and other issues.Two new dynamic sub-frame configuration algorithms in unlicensed bands were proposed and compared with traditional static sub-frame configuration,then the impact of dynamic sub-frame allocation algorithms on system performance was verified by LAA system level simulation platform.The results show that the proposed dynamic sub-frame configuration strategies can effectively improve the resource utilization and the overall system throughput.

Copyright of Computer Measurement & Control is the property of Magazine Agency of Computer Measurement & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Display omitted] • The purification efficiency characteristics and interactions of each catalyst in the integrated aftertreatment system are revealed. • CO and HC basically achieve almost 0 when the DOC temperature is higher than 600 K. • The NO reaction rate is closely related to DOC temperature. • Inlet pressure of DOC has almost no effect on the conversion of HC and CO. • When the temperature is higher than 500 K, the NOx conversion efficiency of SCR is very high. In this paper, the emission characteristics and catalytic reactors interactions of a non-road diesel engine are investigated under non-road transient cycle (NRTC) by experiment and system level simulation. The results showed that the overall emission conversion efficiency of hydrocarbon (HC), carbon monoxide (CO), nitrogen oxides (NO X) and particulate matter (PM) is 96.68 %, 91.45 %, 97.67 % and 93.33 %, respectively under NRTC in experiment. In addition, the interactions of each catalytic converter for emissions under NRTC have been obtained through simulation. When the diesel oxidation catalytic (DOC) temperature is higher than 600 K, CO and HC emissions basically achieve almost 0 through DOC purification. Furthermore, DOC can convert nitric oxide (NO) into nitrogen dioxide (NO 2) which provides strong oxidation for the passive regeneration of diesel particulate filter (DPF). The NO reaction rate is closely related to DOC temperature. And the average conversion efficiency from NO to NO 2 in DOC is 40.36 %. Moreover, the DOC inlet pressure has almost no effect on the conversion of HC and CO. When the temperature of selective catalytic reduction (SCR) is higher than 500 K, the averages NOx conversion efficiency of SCR is up to 98.74 %. And ammonia purification catalyst (ASC) can further reduce NO emissions while absorbing slip ammonia. When the inlet temperature of DPF is more than 520 K, it has almost no effect on the oxidation of PM. The PM conversion efficiency of aftertreatment system (ATS) is mainly affected by the PM collection efficiency of DPF. The average PM collection efficiency of DPF is 53.32 %, while the PM conversion efficiency of ATS is 91.54 % by simulation. Although DPF will convert PM to CO, these CO cannot be completely converted into carbon dioxide (CO 2). So the CO conversion efficiency of ATS is lower than that of DOC. [ABSTRACT FROM AUTHOR]

In dense heterogeneous wireless network, the large-scale small cell deployment can substantially increase not only the complexity of the interference environment but also the network energy consumption. Based on the system model and deployment scenario of small cell enhancement, the energy efficiency in dense heterogeneous wireless network was analyzed and simulated from the sight of system level under different scenarios with different pico numbers. The evaluation has profound guiding significance for the future energy efficiency analysis and optimization in dense heterogeneous wireless network.

The 3rd Generation Partnership Project (3GPP) has recently developed device-to-device (D2D) communication to cope with the explosively increasing mobile data traffic. The D2D communication uses sidelink that is based on the single-carrier frequency-division multiple access scheme because of its low peak-to-average power ratio. In addition, the demodulation reference signal is designed to support multiple input multiple output. In this paper, we propose a DFT-based channel estimation scheme for sidelink in D2D communication. The proposed scheme uses the two-dimensional minimum mean square error interpolation scheme for a user moving at a high speed. We performed a system level simulation based on 20-MHz bandwidth of the 3GPP LTE-Advanced system. Simulation results show that the proposed channel estimation scheme has improved signal-to-interference-plus-noise ratio, throughput, and spectral efficiency as compared with a conventional scheme. [ABSTRACT FROM AUTHOR]

In this paper, we propose a channel estimation scheme for a long term evolution-advanced (LTE-A) downlink system. The proposed scheme uses the fast Fourier transform (FFT) interpolation scheme for the user moving at a high speed. The FFT interpolation scheme converts the channel frequency response obtained from the least square or minimum mean square error channel estimation scheme to a time-domain channel impulse response by using the inverse FFT (IFFT). After windowing the channel response in the time domain, the channel frequency response can be obtained using the FFT. We performed a system-level simulation based on the 20 MHz bandwidth of the 3rd Generation Partnership Project LTE-A downlink system. Simulation results show that the proposed channel estimation scheme can improve the signal-to-noise-plus-interference ratio, as well as the throughput and spectral efficiency, of a conventional system. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Posts & Telecommunications (Natural Science Edition) is the property of Chongqing University of Posts & Telecommunications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The third Generation Partnership Project (3GPP) Long-Term Evolution (LTE) is becoming the first truly global wireless communication standard. LTE system is expected to have an ability to sense the wireless environment. To evaluate the performance of cognitive LTE network, the design of system level simulation platform is proposed. This platform realizes relevant spectrum sensing algorithm and dynamic spectrum allocation strategy. The architecture of this simulation platform is introduced. Based on LTE system level simulator, cognitive radio function is implemented and five modules are developed, including spectrum sensing module, spectrum allocation module, spectrum switching module, link adaptation module, link-system interface module. Class diagram of the simulation platform is also given in this paper. Simulation flow chart introduces the working mechanism in detail. Finally network performance of cognitive LTE system, including average throughput, average spectral efficiency, detection probability, false alarm probability, miss alarm probability, is evaluated using this platform. [ABSTRACT FROM AUTHOR]

To implement high-order multiuser multiple input and multiple output (MU-MIMO) for massive MIMO systems, there must be a feedback scheme that can warrant its performance with a limited signaling overhead. The interference-to-noise ratio can be a basis for a novel form of Codebook (CB)-based MU-MIMO feedback scheme. The objective of this paper is to verify such a scheme's performance under a practical system configuration with a 3D channel model in various radio environments. We evaluate the performance of various CB-based feedback schemes with different types of overhead reduction approaches, providing an experimental ground with which to optimize a CB-based MU-MIMO feedback scheme while identifying the design constraints for a massive MIMO system. [ABSTRACT FROM AUTHOR]